When we say "charge" in an atom, we use a number that determines the electromagnetic interactions of the atom. In Iron (II) oxide, or Ferrous Oxide, or FeO, the Iron element (Fe) is bonded to the Oxygen, in the oxidation state of "2". This means that the Iron has accepted 2 electrons from the Oxygen. Because of this electromagnetic interaction, the charge of the Iron (Fe) in FeO is 2+.

Remember that oxidation describes the loss of an electron by a molecule or atom. In FeO, you have one atom of Fe with 2 extra protons (+charge), and the Oxygen is an atom with two extra electrons (-charge). Both atoms will attract to each other because of their fundamental force of nature, the electromagnetic interaction.

Can you figure out what is happening in the next reaction known as rusting?